The invention relates to a luminaire suitable for accommodating a light source which lies substantially in a first plane, comprising an optical element which lies substantially in a second plane, while said optical element is provided at one side or both sides with facets having different inclination angles, which facets are formed mainly by parallel prisms. The invention is also concerned with an optical element suitable for use in such a luminaire.
Such a luminaire is known from DE-A-43 05 585. A collimated light beam can be made to change its direction by means of such a luminaire. Facets may be used in two different ways for this purpose. A first way is that refraction occurs at the facets. This applies to a deflection of the light by an angle of at most 30xc2x0. A second way is that a full internal reflection takes place at a surface of the facets. This is a suitable way for achieving deflection angles of between 25xc2x0 and 90xc2x0. It is possible by means of a matrix of such facets to form a plurality of beams which shine in different directions. At a longer distance, these beams merge (are superimposed), which renders it possible to make a beam of any shape whatsoever. It is thus possible to achieve a highly complex and accurate light distribution as desired by a user. It is even possible to project a text with such a matrix.
It is very difficult, however, to manufacture such a matrix of facets. This situation can be strongly improved in that the matrix is built up from a number of rows of facets, the facets of each row enclosing a fixed angle, which lies in a third plane perpendicular to the row and perpendicular to the second plane, with a perpendicular on the second plane, and enclose an angle with said perpendicular in a fourth plane through the row which is perpendicular to the second plane, which angle changes progressively along the row from one facet to the next. The fixed angle in the third plane varies from row to row. The optical element has a sawtooth structure in an embodiment, the facets being formed by substantially parallel prisms. In this case a prism preferably has curved sides, as seen in a direction in the plane of the optical element. Such prisms can be provided on a lens or a lens mold in a simple manner by means of a shaping tool. An optical element thus formed for a luminaire is suitable for shaping medium-wide beams and can be industrially manufactured in a reliable manner in batch production.
Problems arise, however, when beams of large deflection angles are to be formed. A first problem is that the required angle variation in the fourth plane leads to the formation of steeply rising rows which in their turn give rise to the formation of an impractically large height of the optical element. A second problem is that light fully reflected in facets of a first row is intercepted by a second, adjoining row under certain circumstances owing to the increasing dimensions of the prisms of consecutive rows. A shadow effect of one or several rows will then arise.
The invention has for its object to solve the above problems. According to the invention, a luminaire of the kind mentioned in the opening paragraph is for this purpose provided with an optical element in which consecutive facets of a row form a surface which is alternately concave and convex in shape. An advantage of this is that the overall construction of the optical element requires a smaller height. A further improvement can be realized in that consecutive rows are situated at mutually differing distances from the second plane. A further improvement in the prevention of shadow effects can be achieved when those rows from among consecutive rows of facets for the purpose of full internal reflection which have a greatest fixed angle are at a greatest distance to the second plane. An improved beam formation of the light issuing from the luminaire can thus be realized, while the advantage of comparatively small dimensions of the optical element is retained.
In a preferred embodiment of the luminaire, the light source comprises a plurality of light sources. Preferably, the light sources are collimated light sources. The formation of parallel beams from the light of the plurality of light sources, by means of reflection and/or refraction, before this light hits the optical element renders it possible to achieve an accurate light distribution of the output beam. Highly suitable light sources are light-emitting diodes (LEDs).